This invention relates generally to methods and apparatus for efficiently heating biological tissues with high intensity ultrasound for therapeutic purposes, and in particular, to endoscopic devices for applying ultrasound energy to uterine fibroids and other pathologic tissues that are inside body or organ cavities, to destroy the tumor or the diseased tissue.
Fibroids are benign tumors in women""s uteri. There are different types of fibroids, including submucosal, which are inside the uterine cavity; intramural, which are in the uterine wall; and subserosal, which are outside the uterus. Fibroids may cause excessive bleeding and pain. For symptomatic fibroids, surgery is the predominate treatment. Every year in the U.S., there are more than 200,000 cases of fibroid-caused hysterectomies. To preserve the uterus, the patient may choose myomectomy, which removes the fibroids only. There are more than 80,000 abdominal myomectomies each year in the U.S. These surgical procedures cause significant trauma to the patients and result in significant costs. Consequently, patients need several days of hospital stay and suffer from the prolonged recovery.
Minimally invasive surgical (MIS) procedures have been explored to treat uterine fibroid trans-abdominally or trans-cervically under laparoscopic or hysteroscopic guidance. Many MIS apparatus have been developed to make the procedure less difficult. Several prior art devices are described in U.S. Pat. No. 5,304,124; U.S. Pat. No. 5,662,680; and U.S. Pat. No. 5,709,679. Besides surgically resecting and removing the tumor tissue, alternative treatments include using different energy forms, such as laser, radio frequency (RF), and cryo-therapy, to thermally ablate or necrose the fibroid tissue. Most of these techniques require the insertion of needles or other types of devices into the body of the fibroid. The mechanical damage to the fibroid and the uterus can cause bleeding during the treatment and adhesions after the treatment. Suturing the damage in the uterus is very difficult in the laparoscopic MIS procedure. Also, most of these alternative treatments are time consuming and technically challenging.
Uterine arterial embolization (UAE) has been investigated as an alternative treatment for uterine fibroids. In UAE, a catheter is inserted into the patient""s femoral artery. The catheter is then advanced until its tip reaches the uterine artery. Many small particles are then injected into the uterine artery to block the blood flow. Both left and right uterine arteries are treated. Blood vessels supplying uterine fibroids are typically larger than the vessels in the normal uterine tissue. With properly sized particles, the blood vessels feeding the uterine fibroids are embolized, but not those in the normal uterine tissue. The fibroids then starve and die due to lack of a blood supply. The uterus survives, however, on the blood supplied from the ovarian artery and other collateral circulation. The embolization procedure may cause severe pain in the first few days after the treatment. Other disadvantages of UAE may include long X-ray radiation exposure during the procedure and other long-term potential adverse effects. The procedure is not recommended if the patient seeks a future pregnancy.
Ultrasound is a term that refers to acoustic waves having a frequency above the high limit of the human audible range (i.e., above 20 KHz). Ultrasound waves have the capability of penetrating into the human body. Based on this property, ultrasound in the frequency range of 2-20 MHz has been widely used to image internal human organs for diagnostic purposes. Ultrasound imaging has also been suggested as a tool for guidance during a resectoscopic surgery (U.S. Pat. No. 5,957,849).
When ultrasound energy is absorbed by tissue, it becomes thermal energy, raising the temperature of the tissue. To avoid thermal damage to tissue, the power level in diagnostic ultrasound imaging is kept very low. The typical ultrasound intensity (power per unit area) used in imaging is less than 0.1 watt per square centimeter. High intensity focused ultrasound, which can have an intensity above 1000 watts per square centimeter, can raise the tissue temperature at the region of the spatial focus to above 60-80 degrees Celsius in a few seconds and can cause tissue necrosis almost instantaneously.
High intensity ultrasound has been proposed to treat and destroy tissues in the liver (G. ter Haar, xe2x80x9cUltrasound Focal Beam Surgery,xe2x80x9d Ultrasound in Medicine and Biology, Vol. 21, No. 9, pp.1089-1100, 1995); in the prostate (N. T. Sanghvi and R. H. Hawes, xe2x80x9cHigh-intensity Focused Ultrasound,xe2x80x9d Experimental and Investigational Endoscopy, Vol. 4, No. 2, pp.383-395, 1994); and in other organs. In U.S. Pat. Nos. 5,080,101, 5,080,102, 5,735,796, 5,769,790, and 5,788,636, for example, ultrasound imaging is combined with a high intensity ultrasound treatment to target the treatment region and to monitor the treatment process. In U.S. Pat. Nos. 5,471,988, 5,492,126, 5,666,954, 5,697,897, and 5,873,828, endoscopic ultrasound devices with both imaging and therapeutic capabilities are disclosed. These devices all have an elongated tube or shaft, so that they can be inserted in organ cavities (e.g., into the rectum) or into the abdominal cavity through a puncture hole in the abdominal wall to bring the ultrasound imaging and treatment sources closer to the disease sites. Some of them have flexible ends, which can be bent to fit the anatomy of a specific patient.
The therapeutic ultrasound beam is focused inside tissue to a small spot of a few millimeters in size. At the focus, tissue temperature rapidly exceeds a level sufficient to cause tissue necrosis, thus achieving the desired therapeutic effect. Outside of the focus, ultrasound energy is less concentrated, tissue temperature rise remains below the necrosis level during the typically short exposure times employed. To treat a tissue volume larger than the focal spot, in the prior art, the ultrasound focus is deflected mechanically or electronically to scan, or incrementally expose, the target tissue volume. One disadvantage of the current high intensity ultrasound therapy is its inefficiency when treating large tumors or heating a large volume of tissue. Even though a three-second ultrasound pulse can increase the temperature of tissue at its focus dramatically, the ultrasound treatment must typically pause 40-60 seconds between two subsequent pulses to allow the intermediate tissue between the focus and the ultrasound transducer to cool sufficiently to avoid thermally damaging the tissue. The volume of tissue necrosis for each treatment pulse is very small (xcx9c0.05 cm3). For example, to treat a volume of tissue within a 3 cm diameter sphere, it will take more than 4 hours, too long to be practical in most clinical situations. Many symptomatic uterine fibroids are larger than 2-3 cm in diameter, and multiple fibroids are also common. To be acceptable for clinicians and patients, the ultrasound treatment time must be significantly reduced.
Large device size is the second disadvantage of the therapeutic ultrasound apparatus in much of the prior art. Most of these devices have two separated ultrasound transducers, including one for imaging and the other for therapy. For effective treatment, the diameter of the treatment transducer is approximately equal to the maximum depth, where the f-number (transducer diameter divided by its focal length) of the transducer is about one (f/1). The transducer surface area must also be sufficiently large to generate high ultrasound power. In some prior art endoscopic devices (for example, in U.S. Pat. Nos. 5,471,988 and 5,873,828), there is a large orifice in the center of the therapy transducer for positioning an imaging transducer. This orifice reduces the area of the treatment transducer and increases its effective f-number. In this case, the size of the treatment transducer must be increased to maintain its effectiveness, so that the overall dimensions of the device are increased. For endoscopic (trans-cervical or trans-abdominal) uterine fibroid treatments, the maximum acceptable diameter of an ultrasound device is about 10 mm. It is seen that it is very difficult to meet this requirement with the large two-transducer configuration.
There is another disadvantage of the two-transducer configuration in which there is an orifice in the center of the treatment transducer. In endoscopic uterine fibroid treatment, the ultrasound device is directly brought against the surface of the fibroid tumor. The tumor surface near the orifice of the transducer will not be treated unless the transducer is moved away or aside from its initial position. Oftentimes, the space is very limited, especially inside the uterus. There may not be sufficient space to permit the device to move, a limitation that results in incomplete treatment of the tumor.
What is needed is a minimally invasive or noninvasive device for treating uterine fibroids. The device should preferably cause minimal or no trauma to the patient body so that the patient requires minimum or no recovery time; it should be easy to use; and, the treatment should be quickly administered. The device should preferably not cause blood loss during the treatment procedure; it should not mechanically damage the treated organ (e.g. uterus) to avoid the need for complicated organ repair (such as suturing or extensive cauterization); and, it should not increase the risk of post-operative adhesions and other complications. In addition, the device should be capable of carrying out the following functions:
(1) Ultrasonically increase the tissue temperature in the uterine fibroid to cause tumor necrosis. Shrinkage of the necrosed tissue will reduce the blood supply to the tumor. This occlusion effect will further reduce the chance of survival for the tumor.
(2) Significantly reduce the ultrasound treatment time and thereby improve physician and patient acceptance. A positive feedback heating process can be provided to efficiently and rapidly raise the temperature in a large volume of tissue.
(3) Combine the ultrasound imaging and therapy transducer in one to enable the -dimensions of the apparatus to be more compact so that the device can be inserted into patient""s uterine cavity or permit practical laparoscopic use (e.g., be inserted trans-abdominally).
(4) Include a treatment transducer that does not have an orifice in its center, so that the tumor tissue can be treated thoroughly.
(5) Provide ultrasound imaging capability for treatment guidance. The imaging capability should provide real-time assessment of the anatomy before, during, and after the treatment. Doppler imaging can be advantageously employed to aid targeting and the assessment of treatment.
(6) Use ultrasound to detect and differentiate the tissue property changes before and after the treatment to make an assessment of the treatment result possible.
(7) Create an acoustic absorption barrier inside the treated tissue to prevent the tissue beyond the desired treatment zone from being thermally damaged.
(8) Provide a feedback control mechanism to turn the treatment transducer element off when the transducer is not properly coupled to the tissue to prevent the device from being damaged by reflected ultrasound power.
(9) Provide an effective cooling mechanism to prevent the device from being thermally damaged.
(10) Use an ultrasound contrast agent (micro-bubbles) to enhance the treatment effect.
(11) Provide effective means to acoustically couple an ultrasound source to targeted tissue structures.
(12) Use elasticity imaging to assess the state of tissues prior, during, and after ultrasonic treatment.
(13) Employ cavitation as a therapeutic means to necrose selected tissues.
Currently, an endoscopic ultrasound probe is not available that can provide the above-noted functions. Accordingly, it will be apparent that both such a device and an effective and efficient method for treating uterine fibroid tumors and other internal tissues and diseased tissue masses is needed that overcomes the problems with prior art apparatus and methods.
The present invention is directed to a method and apparatus for efficiently treating uterine fibroids and other diseases with high intensity ultrasound, where the apparatus is small enough to fit in the limited space in a patient organ cavity or a limited puncture size on an abdominal wall.
Specifically, an ultrasonic system for destroying undesired tissue at an internal site within a body of a patient includes a probe that is sized to be inserted within a body of a patient. An ultrasonic transducer is mounted proximate a distal end of the probe and is adapted to couple to a power supply used to selectively energize the ultrasonic transducer so that it produces a focused beam of high intensity ultrasonic energy. An ultrasound transmissive interface is coupled to the distal end of the probe and is disposed and adapted to conform to a surface of the undesired tissue. The interface provides a liquid layer that more efficiently transmits the high intensity ultrasonic energy produced by the ultrasonic transducer into the undesired tissue. The high intensity ultrasonic energy increases a temperature of the undesired tissue sufficiently to cause the tissue to necrose.
In one form of the invention, the ultrasound transmissive interface comprises an elastomeric cavity that is adapted to contain a liquid. The elastomeric cavity is disposed between the ultrasonic transducer and the surface of the undesired tissue so that the high intensity ultrasonic energy passes through the liquid within the elastomeric cavity and into the undesired tissue. The elastomeric cavity is formed at least in part from a semi-permeable membrane, so that the liquid from within the elastomeric cavity weeps onto a surface of undesired tissue to increase the efficiency with which the high intensity ultrasonic energy is coupled into the undesired tissue.
In another form of the present invention, the ultrasound transmissive interface comprises a cap made of an elastomeric material, which is disposed to surround the ultrasonic transducer. The cap is adapted to seal against the undesired tissue and to contain a liquid that increases an efficiency with which the high intensity ultrasonic energy is coupled into the undesired tissue. In addition, the cap preferably includes a rim having a double lip seal formed around a perimeter. A passage in the cap is adapted to couple the double lip seal to a vacuum line so that the rim of the cap is held against a surface of the undesirable tissue, sealing the liquid inside of the cap.
Another aspect of the present invention is directed to a method for administering an ultrasonic therapy to destroy at least a portion of an undesired tissue mass. The method includes the steps of providing an ultrasonic transducer that emits a focused high energy ultrasonic energy when energized, and positioning the ultrasonic transducer proximate the undesired tissue mass. The ultrasonic transducer is directed toward a desired focal point within the undesired tissue mass. Then, the ultrasonic transducer is energized so that it emits the focused high energy ultrasonic energy at the desired focal point, causing necrosis of a portion of the undesired tissue mass disposed at the desired focal point. At least one of an f-number, an intensity, a time, and a direction of the high intensity ultrasonic energy emitted into the undesired tissue mass is controlled to achieve a desired shape and size of a necrotic zone of undesired tissue, destroyed as a result of being heated by the high intensity ultrasonic energy. The necrotic zone substantially blocks the high intensity ultrasonic energy from penetrating beyond the necrotic zone. The desired shape and size of the necrotic zone are preferably selected and formed so as to cause substantially all of the undesired tissue mass to ultimately be destroyed.
The step of controlling preferably includes the step of repositioning the ultrasonic transducer to direct the high intensity ultrasonic energy at a different portion of the undesired tissue mass, to achieve the desired shape and size of the necrotic zone. In one application of the method, the desired shape and size of the necrotic zone are selected so that formation of the necrotic zone substantially deprives the undesired tissue mass of a blood supply, causing the ultimate destruction of the undesired tissue mass. In another application of the method, the desired shape and size of the necrotic zone are selected to control bleeding at a treatment site.